Closure systems are used to protect internal components from degradation caused by external environments. For example, internal components such as fiber optic cables and copper cables are often enclosed in closure systems. Examples of commercially available closure systems include the Outdoor Fiber Drop Repair (OFDR), the Outdoor Fiber Distribution Closure (OFDC), and the Fiber optic Infrastructure System Technology (FIST), available from Tyco Electronics, Kessel-Lo, Belgium. In particular, the OFDR Closure is used to break out fibers from a looped fiber optic cable to connect users such as business customers or persons in multiple or single living units. These types of closures can be used in aerial, pedestal, and underground environments. Other closure systems are commercially available for use with communication and energy transmission cables.
Closure systems typically include internal components such as fiber organizers, cable seals and termination devices, drop cable seals for a number of drops with drop cable termination devices, and universal splice holders for a number of splices. These internal components may be subject to environmental factors such as varying moisture levels, heat and cold, and exposure to other chemical substances. The closure systems are preferably protected from damage with a sealant of some sort. Conventional sealants, however, suffer from a number of drawbacks that make them unsuitable for certain closure systems.
Sealants are often used for insulation and for protection against water, corrosion and environmental degradation, and for thermal management. Prior to now, a number of sealants have been known; however, currently available sealants have certain drawbacks and disadvantages that make them inadequate for specific uses and for use in contact with certain materials. In particular, there is an unmet need for sealants that are suitable for fiber optic and electronic closure systems.
Suitable sealing systems for closures are needed for use with a variety of different cables. For examples, a sealing system is needed for cables termed Low Smoke Zero Halogen (“LSZH”), also known as Low Smoke Halogen Free (“LSHF”), Low Smoke Zero Halogen (“LSOH”), and Zero Halogen Low Smoke (“OHLS”) among other things.
LSZH cables are characterized by containing no halogenated flame-retardants, and produce relatively limited amounts of smoke when exposed to sources of heat such as a flame or heated wires. LSZH cables provide an alternative to the frequently used polyethylene, PVC, or thermoplastic urethane coatings. Polyethylene, PVC, or thermoplastic urethane, when they contain halogens, may produce hazardous halogen-containing compounds such as HCl or HBr gas. An improvement to current LSZH cable closure systems is needed to enhance performance in environmentally sensitive environments.
Traditionally, thermoplastic oil gels have been used in LSZH closure systems. A problem, however, with thermoplastic gels used as sealants, and in closure systems in general, is that they often contain high amounts of mineral oil. A problem has been observed with oil-containing gels in that they may leak oil. The oil in these gels may leak from the gel and cause deterioration, discoloring, or degradation of the cable in the closure system. In some extreme cases, a cable may even snap under compression due to the damage done by the oil leaking from the thermoplastic gel. There exists an unmet need for alternatives to oil containing gels. Presently available alternatives to oil-containing gels, however, have not provided such a solution. For one, sealants other than oil-containing gels may have one or more undesirable properties. Examples of undesirable properties include excessive hardness, inadequate temperature resistance (e.g., flammability or a tendency to become brittle with cold, i.e., inadequate glass transition temperature) and viscoelastic properties, chemical incompatibility, high water absorption, and hydrolytic instability. Accordingly there exists an unmet need for closure systems with suitable hardness, viscoelastic properties, low permanent set or compression set, long-term performance (e.g., >20 years), amongst other properties.
In contrast to oil-containing thermoplastic gels, dry silicone thermoset gels contain relatively low, or do not contain at all, amounts of diluent fluids such as unreactive silicone oil or mineral oil. A dry silicone gel, instead of being a thermoplastic gel, is a thermoset gel. Thermoset gels can be produced by chemical crosslinking. Examples of thermoset gels are silicone dry gels and polyurethane gels. A dry silicone gel makes no use of an extra solvent or diluent fluid but can still be categorized under the term “gel” because of the similarity in physical properties and behavior, or because of its viscoelastic properties. Dry silicone gels are however used more rarely than free oil-containing gels for a number of reasons. For example, dry silicone gels are rare because they are more expensive and difficult to process than certain other types of gels. Accordingly, there exists an unmet need for an improved dry silicone gel and an improved method of preparing a dry silicone gel.
U.S. Pat. No. 7,489,844 discloses fiber optic cable with a suspension liquid surrounding the optical fiber. The suspension oil may be mineral oil or a blend of oil and silica.
U.S. Pat. No. 6,091,871 discloses a reinforced optical fiber cable that includes a protective tube for protecting optical fibers, a reinforcing layer, and reinforcing rods around the protective tube, together with an outer sheath. The inside space in which the optical waveguides are received contains a filler material to protect the optical waveguides against penetration of moisture.
U.S. Pat. No. 6,167,178 discloses a fiber optic cable including at least one optical fiber having a buffer layer formed of a flame-retardant polyolefin material. The flame-retardant polyolefin material is tightly formed about the optical fiber, thereby defining a tight buffer layer, a layer of strength members, and a cable jacket surrounding optical fibers in contact with at least some strength members.
U.S. Pat. No. 7,522,795 discloses a loose tube optical waveguide cable with two or more optical waveguides with a single protective tube, or sheath for environmental protection. The cable contains no gel-like compounds and no strengthening elements.